Unlike the right heart cavities for which it is sufficient to implant endocardial leads via the right peripheral venous network, the implantation of permanent leads into a left heart cavity involve substantial surgical risks, such as the risk of bubbles passing to the cerebral vasculature located downstream of the left ventricle. For this reason, when the stimulation of a left cavity is chosen, most often a stimulation lead is introduced, not into the cavity to be stimulated, but instead in the coronary network, the lead being provided with an electrode that is applied against the wall of the epicardium and oriented toward the left ventricle or the left atrium, as appropriate. These leads typically stimulate the heart muscle via one or more point electrodes whose position depends on the predefined trajectory of the cannulated vein.
A commercial lead of this type is, for example, the Situs LV model, sold by Sorin CRM (Clamart, France) and described in EP 0993840 A1 and its counterpart U.S. Pat. No. 6,385,492 (both assigned to Sorin CRM S.A.S., previously known as ELA Medical).
The U.S. Pat. Publication No. 2008/0039916 A1 and U.S. Pat. No. 5,755,735 A disclose additional examples of such leads implanted in the coronary system. The U.S. Pat. Publication No. 2011/0072659 A1, meanwhile, discloses another type of lead for deep brain stimulation.
The introduction of such a lead is via the coronary sinus, from its opening in the right atrium. The lead is then pushed and oriented along the network of the coronary veins to the selected site. This procedure is very delicate, given the peculiarities of the venous system and its access paths, including the passage of valves and tortuosities as well as the gradual reduction of the venous diameter as the lead progresses along the selected coronary vein(s).
Once the target vein is reached, the surgeon looks for a satisfactory stimulation (pacing) site, one with good electrical contact of the stimulating electrode against the tissue of the epicardium, this contact having to be maintained despite the various variations or stresses over time.
It has been proposed to have multiple electrodes along the lead body to increase the chances of an acceptable compromise, by possibly giving to the body of the lead a particular conformation. The surgeon can thus select, among the various electrodes present on the lead body, the one providing the best efficiency from both the electrical and hemodynamic points of view. Such a multi-electrode lead is described in EP 1938861 A1 and its counterpart U.S. Pat. Publication No. 2008/0177343 (both assigned to Sorin CRM S.A.S., previously known as ELA Medical) and in the U.S. Pat. Publication No. 2008/0039916 above.
These leads implement the concept of “electronic repositioning”, directing or redirecting the electric field between different electrodes arranged along the pacing lead of the left ventricle and/or with one of the electrodes of the pacing lead of the right ventricle. This technology allows the management of micro-movements or changes in the hemodynamic behavior (reverse modeling), simply by reprogramming the implanted device generator via telemetry through the skin, without the burden of reoperation or further surgical intervention.
The counterpart of this solution is an increasing complexity of the structure of the lead. However, increasing the number of electrodes causes an increase in the number of components, and therefore of electrical connections, or requires the use of multiplexing circuits for the selection of the various electrodes present on the lead. All this leads to an increased risk of mechanical failure.
U.S. Pat. Publication No. 2009/157136 A1 describes a technique for finding an optimal pacing site using a temporary mapping catheter to be introduced into the coronary sinus. This catheter is either a flexible tube open at both ends, or a guidewire. In either case, it includes multiple electrically independent distal electrodes, and in the proximal portion a connector for connecting to an acquisition system for identification of the best stimulation site using an algorithm based on cardiac motion. A classic permanent definitive multielectrode lead of standard diameter from 4.5 to 6 French (1.5 to 2 mm) is then placed to the selected position, by use of a guide wire and the over the wire (OTW) technique or a tube (lumen) of the temporary catheter.
Another trend of recent developments in the field of pacing the left ventricle is the reduction of the diameter of the portion implanted in the coronary network, to a diameter of 4 French (1.33 mm). The size of the lead body is indeed a factor directly related to the controlled guiding capabilities of the lead into the coronary venous system, in order to be able to select specific stimulation sites located in certain collateral veins. These sites are reached by means of a vein sub-selection catheter used for the introduction of a guiding stylet to the chosen site. Once the vein is selected and stylet is introduced, the surgeon advances the lead body that slides over the stylet, the latter acting as a support wire of small diameter axially guiding the lead body to the selected location (OTW technique).
The above U.S. Pat. Publication No. 2008/0039916 A1 proposes to reduce the distal end portion to a diameter comprised between 1 and 5 French. Nevertheless, the multiplication of the electrodes and of the components or internal conductors necessarily implies an increase in the diameter of the lead body and reduces its flexibility, making it difficult or impossible to pass the tortuosities, which goes against the use of a small diameter and of a very high distal flexibility, features that are required in order to achieve implantation in the deepest collateral veins.